Impact Electronic Transformer Insulating Varnish The main factors include: temperature, humidity, oil protection method, and overvoltage.

　　1. The influence of temperature.

　　Power transformers use oil-paper insulation, and the moisture levels in the oil-paper exhibit different equilibrium curves depending on temperature. Generally speaking, as temperature rises, moisture from the paper tends to migrate into the oil reservoir—essentially "settling" there—while the paper itself absorbs water from the oil. Consequently, at higher temperatures, the insulating oil inside the transformer contains a higher concentration of dissolved moisture; conversely, at lower temperatures, the moisture content in the oil remains relatively low.

　　The degree of cellulose cyclization and chain scission, as well as gas production, varies with temperature. At a specific temperature, the rates of CO and CO formation remain constant, meaning the concentrations of CO and CO gases in the oil increase linearly over time. However, as the temperature continues to rise, the rates of CO and CO generation begin to grow exponentially. Consequently, the levels of CO and CO in the oil are directly linked to the thermal aging of the insulating varnish in oil-filled transformers, making changes in their concentration a reliable indicator of potential abnormalities in the paper layers within sealed transformers.

　　The lifespan of a transformer depends on the degree of aging of the insulating varnish used in its electronic components, and insulation aging is directly influenced by operating temperature. For oil-immersed transformers running at rated load, the average winding temperature rises to 65°C, while the hottest spot can reach up to 78°C. If the average ambient temperature is 20°C, the hottest point could climb to 98°C. Under these conditions, the transformer can typically operate reliably for 20 to 30 years. However, if the transformer is overloaded, its temperature will increase further, significantly reducing its expected service life.

　　2. The impact of humidity.

　　The presence of moisture accelerates the degradation of cellulose in paper. Consequently, the production of CO and CO₂ is also linked to the water content in cellulose materials. At a given humidity level, the higher the moisture content, the greater the decomposition of CO; conversely, the lower the moisture content, the more CO decomposes.

　　Moisture present in trace amounts in electronic transformer insulation coatings is one of the key factors affecting insulation performance. Similarly, even tiny amounts of water in insulating oil can severely compromise the electrical and physicochemical properties of the insulating medium. Moisture reduces the spark-over voltage of insulating oil, increases the dielectric loss factor (tan δ), accelerates the aging process of the oil, and ultimately degrades its insulating capabilities. Moreover, when equipment becomes damp, it not only diminishes the reliability and lifespan of power devices but can also lead to equipment failure—and, in extreme cases, even pose serious risks to personal safety.

　　3. The impact of the oil protection method.

　　Oxygen in transformer oil accelerates insulation decomposition reactions, and its concentration depends on the method used to protect the oil. Additionally, different oil-layer protection techniques influence how CO and CO₂ decompose and diffuse within the oil. If the solubility of CO is low, it tends to easily escape into the airspace above the oil surface in open-type transformers, resulting in a CO volume fraction that typically does not exceed 300 ppm. In contrast, sealed transformers prevent CO and CO₂ from volatilizing due to the insulating barrier between the oil surface and air, leading to significantly higher concentrations of these gases.

　　4. The impact of overvoltage.

　　During normal operation, the phase-to-ground voltage of a three-phase transformer is 58% of the phase-to-phase voltage. However, in the event of a single-phase fault, the main insulation voltage rises by 30% in neutral-grounded systems and by as much as 73% in neutral-ungrounded systems, potentially leading to insulation damage.

　　Due to the steep wavefront, lightning overvoltage causes an uneven voltage distribution across longitudinal insulation (turn-to-turn, parallel, and interlayer insulation), potentially leaving discharge marks on the insulation and ultimately leading to the degradation of solid insulation.

　　Because the wavefront of switching overvoltage is relatively flat, the voltage distribution remains nearly linear. When a switching overvoltage wave propagates from one winding to another, it is approximately proportional to the number of turns between the two windings, which can easily lead to degradation and damage of the main insulation or interphase insulation.